The present invention relates to electric arc furnaces and, more particularly, to controlling the gas flow inside the chamber of electric arc furnaces.
Presently electric arc furnaces produce a natural convection flow of hot gases inside the furnace which moves in a substantially donut shaped circular direction. The hot arc induces plasma which initially flares radially away from the electrode. Soon thereafter the plasma and heated gases rise vertically around the electrode. The void caused by the rising hot gases induces gases from the periphery to flow toward the center of the furnace. The resulting circulation causes the temperature of the electrode to rise. The increase in the electrode's temperature leads to an increase in electrode consumption. The vertical flow around the electrode also causes positive pressure on the electrode port which increases emissions. In addition to heating the electrode, the rising hot gases impinge on the refractory surrounding the electrode and causes its premature deterioration.
When the rising hot gases reach the ceiling of the furnace chamber, the gases flow radially towards the periphery and along the ceiling. Since the ceiling is water-cooled, the gases lose valuable heat which could have been used to preheat the metal scrap. Similarly, energy escapes through the off-gas hole which could have instead been used to preheat the scrap.
Methods for controlling hot gas circulation in a furnace chamber have been previously disclosed. For example European Patent Application 0 462 898 A1 injects gas tangentially around the perimeter of a scrap melting electric arc furnace in two counter rotating horizontal planes. German Patent DE 3629055 A1 injects gases into the furnace cavity aiming the gas jets at the cold spots in the furnace, while at the same time injecting gases through injection ports located underneath the liquid metal level. Neither of the two patents teaches generating a circulation pattern which overcomes the above outlined disadvantages.